The concept of an “electronic nose” has been an active area of research for some decades. Researchers have been trying to provide such a device e.g., by attempting to couple an array of chemical odor sensors with a pattern-recognition system. NASA, for instance, has been trying to develop such a nose to detect the presence of gases such as ammonia that may be poisonous to astronauts. Ammonia is integral to life on the space station because it carries heat originating inside the station through pipes outside to space. However, ammonia is poisonous and a leak must be detected quickly and stopped. Humans are only capable of detecting ammonia at about 50 ppm, although it can be dangerous at a concentration of only a few parts per million. A suitable sensor, or electronic nose capable of detecting ammonia at such low concentrations is needed.
Considerable interest has been generated by the Department of Homeland Security about the use of electronic devices in detecting volatile compounds to prevent explosive, chemical, or biological attacks. Screening methods developed to detect explosive or toxic chemicals that may be carried through an airport or seaport are, in many ways, a first line of defense in protecting against such attacks. Such methods currently include laboratory analyses of suspected drugs, drug-sniffing dogs, and the ubiquitous X-ray machine. For most laboratory methods to be performed, a great deal of time must be spent in preparing samples for analysis. Small, portable devices would likely reduce the time needed to detect potential threats. It is greatly desired that sensors used for electronic noses and molecular detection exist and function on a very compact—even molecular—scale and exhibit very good electronic properties.
A significant advance in the art would be to provide chemical sensors that are compact and capable of detecting volatile compounds with all-electronic readout. It is desirable that such sensors be capable of easy modification, in order to provide a wider array of potential sensitivities as well as to be able to enhance the sensitivity to known analytes. Similarly, as the sensors currently available suffer from the major drawback of irreversible adsorption, it is desirable to provide sensors that are capable of self-regeneration in order to prolong the usefulness of the device and save on cost. Also needed are methods of detecting such volatile compounds using a device comprising individual sensors or arrays made of compact chemical sensors.